We have isolated two glycosylated polypeptides from developing human brain. One has MW of 225,000, the other 150,000 (gps 150/225). Both contain PHA-L binding N-linked glycan that contributes 15-20 kd to their sizes. Both contain the HNK-l epitope. Both are easily solubilized without a detergent and both are secreted by cells in tissue culture. Immunohistochemical and immunochemical studies show that one or both of the gps 150/225 are in oligodendrocytes prior to and during myelination but neither one shows up in myelin. We do not find the gps 150/225 in any other cell type in normal tissues. The gp 225, however, shows up in reactive astrocytes in and around active M.S. plaques and relatively recent infarcts and probably also in remyelinating oligodendrocytes in active M.S. plaques. We have also shown that one or both of the gps 150/225 show up in chromatolytic anterior horn cells (AHC) and in axons and Schwann cells of neuropathic peripheral nerves. Hence they appear in reactive or regenerating AHC and in regenerating peripheral nerve. In this application we propose to study further the biology and structure of the gps 150/225. In these studies we shall place an emphasis on a role they may play in the response of AHC and their companion cells to axonal damage. Specifically we propose to: 1. determine whether the gps 150/225 promote extension of neurites, 2. study the appearance of gps 150/225 in chromatolytic AHC, 3. study heparin-binding of the gps 150/225, 4. study cell-binding of gps 150/225, 5. raise a battery of mAbs against the gps 150/225 and 6. elucidate the primary structure of the gps 150/225 by cloning and sequencing specific cDNAs, 7. study the gps 150/225 in spinal cords and peripheral nerves of patients with ALS and various peripheral neuropathies. We hope that these studies will not only tell us more about the gps 150/225 but also about the biology of healthy and sick AHC and peripheral nerves.